As is well known, virtually all electronic components produce some heat energy while operating and are more or less sensitive to extremes of temperature. Therefore, it becomes necessary to the proper operation of any electrical system that heat must be removed from the components before the temperature rises above some critical value. This problem may be particularly difficult to solve when the electronics are part of the avionics of an air-launched missile. The radar components and the associated power supply are particularly copious heat sources, the skin of the missile is subject to extreme temperature variations due to aerodynamic heating and cooling, and the limitations on the size, weight, power consumption, and reliability of the cooling system are severe.
Many missile cooling systems use an expendable liquid which absorbs heat from the electronics by undergoing a phase change from a liquid to a vapor which is vented from the missile. Such systems require large amounts of volume to store the coolant and thus generally require interconnection with a reservoir on the carry aircraft. These interconnections are subject to failure and require large amounts of maintenance. Further, such a system must be re-filled after each test or mission during which the missile is not fired.
Other generalized electronics cooling systems use heat pipes to transfer heat energy to a heat sink. The only large capacity heat sink available to a missile is the surrounding air and even that is unavailable when the temperature of the missile skin is heated above the critical temperature of the electronics. Small capacity heat sinks may be provided internal to the missile, such as heat of fusion storage devices which are well known, but the mass of the material used to store the heat energy limits the amount of heat which can be stored and thus the length of operation of the avionics. U.S. Pat. No. 3,651,865 teaches a cooling system employing heat pipes and a heat of fusion material, but in a system unsuitable for use in a high-performance missile. A missile cooling system is disclosed in copending application Ser. No. 947,672, but this system places severe limits on operation time of the electronics.